Heater

ABSTRACT

A heater assembly includes a plurality of fuel cell stack assemblies which each have a plurality of fuel cells, a fuel inlet, and an air inlet; a fuel supply conduit which communicates fuel to the fuel inlets; and an air supply conduit which communicates air to the air inlets. An orifice is disposed between the fuel supply conduit and the fuel inlet or between the air supply conduit and the air inlet of each fuel cell stack assembly. The plurality of fuel cell stack assemblies are arranged in fuel cell stack assembly groups such that the orifices of each of the fuel cell stack assembly groups are configured to provide a magnitude of restriction that is unique to their respective the fuel cell stack assembly group, thereby providing uniformity of flow of the fuel or the air to the plurality of fuel cell stack assemblies.

TECHNICAL FIELD OF INVENTION

The present invention relates to a heater which uses fuel cell stackassemblies as a source of heat; more particularly to such a heater whichis positioned within a bore hole of an oil containing geologicalformation in order to liberate oil therefrom; and even more particularlyto such a heater where each fuel cell stack assembly includes an orificeconfigured to provide a predetermined restriction to fuel or oxidizingagent supplied to the fuel cell stack assembly; and still even moreparticularly to such a heater where the fuel cell stack assemblies arearranged in fuel cell stack assembly groups such that the predeterminedrestriction for each fuel cell stack assembly group is unique in orderto provide sufficient flow uniformity of fuel or oxidizing agent to eachfuel cell stack assembly.

BACKGROUND OF INVENTION

Subterranean heaters have been used to heat subterranean geologicalformations in oil production, remediation of contaminated soils,accelerating digestion of landfills, thawing of permafrost, gasificationof coal, as well as other uses. Some examples of subterranean heaterarrangements include placing and operating electrical resistanceheaters, microwave electrodes, gas-fired heaters or catalytic heaters ina bore hole of the formation to be heated. Other examples ofsubterranean heater arrangements include circulating hot gases orliquids through the formation to be heated, whereby the hot gases orliquids have been heated by a burner located on the surface of theearth. While these examples may be effective for heating thesubterranean geological formation, they may be energy intensive tooperate.

U.S. Pat. Nos. 6,684,948 and 7,182,132 propose subterranean heaterswhich use fuel cells as a more energy efficient source of heat. The fuelcells are disposed in a heater housing which is positioned within thebore hole of the formation to be heated. The fuel cells convert chemicalenergy from a fuel into heat and electricity through a chemical reactionwith an oxidizing agent. U.S. Pat. Nos. 6,684,948 and 7,182,132illustrate strings of fuel cells that may be several hundred feet inlength. Operation of the fuel cells requires fuel and air to be suppliedto each of the fuel cells and spent fuel (anode exhaust) and spent air(cathode exhaust) must be exhausted from each of the fuel cells. Inorder to do this, a fuel supply conduit and an air supply conduit areprovided such that each extends the entire length of the string of fuelcells to supply fuel and air to each of the fuel cells. Homogeneousdistribution of fuel and air to each of the fuel cells may beproblematic due to the length of the heaters which may be hundreds offeet long to in excess of one thousand feet, thereby resulting inpressure differentials from fuel cell to fuel cell along the length ofthe heater. The pressure differentials may result in variations in fueland air flow to the fuel cells which may not be compatible with thedesired operation of the heater.

What is needed is a heater which minimizes or eliminates one of more ofthe shortcomings as set forth above.

SUMMARY OF THE INVENTION

A heater assembly includes a plurality of fuel cell stack assemblieswhich each have a plurality of fuel cells which convert chemical energyfrom a fuel into heat and electricity through a chemical reaction withan oxidizing agent, each one of the plurality of fuel cell stackassemblies having a fuel cell manifold which 1) receives the fuel withina fuel inlet of the fuel cell manifold and distributes the fuel to theplurality of fuel cells and 2) receives the oxidizing agent within anoxidizing agent inlet of the fuel cell manifold and distributes theoxidizing agent to the plurality of fuel cells; a fuel supply conduit influid communication with the fuel cell manifold of the plurality of fuelcell stack assemblies, thereby communicating the fuel to the fuel inletof the fuel cell manifold of the plurality of fuel cell stack assembliesan oxidizing agent supply conduit in fluid communication with the fuelcell manifold of the plurality of fuel cell stack assemblies, therebycommunicating the oxidizing agent to the oxidizing agent inlet of thefuel cell manifold of the plurality of fuel cell stack assemblies. Eachof the plurality of fuel cell stack assemblies includes an orificedisposed between the fuel supply conduit and the fuel inlet or betweenthe oxidizing agent supply conduit and the oxidizing agent inlet. Theplurality of fuel cell stack assemblies are arranged in fuel cell stackassembly groups such that the orifices of each of the fuel cell stackassembly groups are configured to provide a magnitude of restrictionthat is unique to their respective the fuel cell stack assembly group,thereby providing uniformity of flow of the fuel or the oxidizing agentto the plurality of fuel cell stack assemblies.

Further features and advantages of the invention will appear moreclearly on a reading of the following detailed description of thepreferred embodiment of the invention, which is given by way ofnon-limiting example only and with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

This invention will be further described with reference to theaccompanying drawings in which:

FIG. 1 is an isometric partial cross-sectional view of a heater inaccordance with the present invention;

FIG. 2 is a schematic view of a plurality of heaters of FIG. 1 shown ina bore hole of a geological formation;

FIG. 3 is an end view of the heater of FIG. 1;

FIG. 4 is an axial cross-sectional view of the heater of FIGS. 1 and 3taken through section line 4-4;

FIG. 5 is an axial cross-sectional view of the heater of FIGS. 1 and 3taken through section line 5-5;

FIG. 6 is an axial cross-sectional view of a fuel cell stack assembly ofthe heater of FIGS. 1 and 3 taken through section line 6-6;

FIG. 7 is an elevation view of a fuel cell of the fuel cell stackassembly of FIG. 6;

FIG. 8 is an enlargement of a portion of FIG. 7;

FIG. 9 is an enlargement of a portion of FIG. 8;

FIG. 10 is an isometric view of a flow director of a combustor of theheater of FIG. 1;

FIG. 11 is a radial cross-section view the heater of FIG. 1 takenthrough section line 11-11;

FIG. 12 is an isometric view of a baffle of the heater of FIG. 1;

FIG. 13 is an enlargement of a portion of FIG. 4 showing adjacent fuelcell assemblies;

FIG. 14 is an enlargement of a portion of FIG. 5 showing adjacent fuelcell assemblies;

FIG. 15 is an enlargement of a portion of FIG. 13;

FIG. 16 is an enlargement of a portion of FIG. 14;

FIG. 17 is an alternative arrangement of FIG. 14;

FIG. 18 is a schematic view of a plurality of fuel cell stack assemblygroups shown in a bore hole of a geological formation;

FIG. 19 is an alternative arrangement of FIG. 15; and

FIG. 20 is an alternative arrangement of FIG. 16.

DETAILED DESCRIPTION OF INVENTION

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, a heater 10extending along a heater axis 12 is shown in accordance with the presentinvention. A plurality of heaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n),where n is the total number of heaters 10, may be connected together endto end within a bore hole 14 of a formation 16, for example, an oilcontaining geological formation, as shown in FIG. 2 in order to form aheater assembly 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n). Bore hole 14 maybe only a few feet deep; however, may typically be several hundred feetdeep to in excess of one thousand feet deep and extends from a top endto a bottom end where the top end is considered the end of bore hole 14where bore hole enters formation 16. Consequently, the number of heaters10 needed may range from 1 to several hundred. It should be noted thatthe oil containing geological formation may begin as deep as onethousand feet below the surface and consequently, heater 10 ₁ may belocated sufficiently deep within bore hole 14 to be positioned near thebeginning of the oil containing geological formation. When this is thecase, units without active heating components may be positioned from thesurface to heater 10 ₁ in order to provide plumbing, power leads, andinstrumentation leads to support and supply fuel and air to heaters 10 ₁to 10 _(n), as will be discussed later.

Heater 10 generally includes a heater housing 18 extending along heateraxis 12, a plurality of fuel cell stack assemblies 20 located withinsaid heater housing 18 such that each fuel cell stack assembly 20 isspaced axially apart from each other fuel cell stack assembly 20, afirst fuel supply conduit 22 and a second fuel supply conduit 24 forsupplying fuel to fuel cell stack assemblies 20, a first oxidizing agentsupply conduit 26 and a second oxidizing agent supply conduit 28;hereinafter referred to as first air supply conduit 26 and second airsupply conduit 28; for supplying an oxidizing agent, for example air, tofuel cell stack assemblies 20, and a plurality of combustors 30 forcombusting exhaust constituents produced by fuel cell stack assemblies20. While heater 10 is illustrated with 3 fuel cell stack assemblies 20within heater housing 18, it should be understood that a lesser numberor a greater number of fuel cell stack assemblies 20 may be included.The number of fuel cell stack assemblies 20 within heater housing 18 maybe determined, for example only, by one or more of the followingconsiderations: the length of heater housing 18, the heat outputcapacity of each fuel cell stack assembly 20, the desired density offuel cell stack assemblies 20 (i.e. the number of fuel cell stackassemblies 20 per unit of length), and the desired heat output of heater10. The number of heaters 10 within bore hole 14 may be determined, forexample only, by one or more of the following considerations: the depthof formation 16 which is desired to be heated, the location of oilwithin formation 16, and the length of each heater 10.

Heater housing 18 may be substantially cylindrical and hollow. Heaterhousing 18 may support fuel cell stack assemblies 20 within heaterhousing 18 as will be described in greater detail later. Heater housing18 of heater 10 _(x), where x is from 1 to n where n is the number ofheaters 10 within bore hole 14, may support heaters 10 _(x+1) to 10 _(n)by heaters 10 _(x+1) to 10 _(n) hanging from heater 10 _(n).Consequently, heater housing 18 may be made of a material that issubstantially strong to accommodate the weight of fuel cell stackassemblies 20 and heaters 10 _(x+1) to 10 _(n). The material of heaterhousing 18 may also have properties to withstand the elevatedtemperatures, for example 600° C. to 900° C., as a result of theoperation of fuel cell stack assemblies 20 and combustors 30. Forexample only, heater housing 18 may be made of a 300 series stainlesssteel with a wall thickness of 3/16 of an inch.

With continued reference to all of the FIGS. but now with emphasis onFIGS. 6 and 7, fuel cell stack assemblies 20 may be, for example only,solid oxide fuel cells which generally include a fuel cell manifold 32,a plurality of fuel cell cassettes 34 (for clarity, only select fuelcell cassettes 34 have been labeled), and a fuel cell end cap 36. Fuelcell cassettes 34 are stacked together between fuel cell manifold 32 andfuel cell end cap 36 and are held therebetween in compression with tierods 38. Each fuel cell stack assembly 20 may include, for example only,twenty to fifty fuel cell cassettes 34.

Each fuel cell cassette 34 includes a fuel cell 40 having an anode 42and a cathode 44 separated by a ceramic electrolyte 46. Each fuel cell40 converts chemical energy from a fuel supplied to anode 42 into heatand electricity through a chemical reaction with air supplied to cathode44. Further features of fuel cell cassettes 34 and fuel cells 40 aredisclosed in United States Patent Application Publication No. US2012/0094201 to Haltiner, Jr. et al. which is incorporated herein byreference in its entirety.

Fuel cell manifold 32 receives fuel, e.g. a hydrogen rich reformatewhich may be supplied from a fuel source illustrated as fuel reformer48, through a fuel inlet 50 from one or both of first fuel supplyconduit 22 and second fuel supply conduit 24 and distributes the fuel toeach of the fuel cell cassettes 34. Fuel cell manifold 32 also receivesan oxidizing agent, for example, air from an oxidizing agent sourceillustrated as an air supply 54, through an air inlet 52 from one orboth of first air supply conduit 26 and second air supply conduit 28.Fuel cell manifold 32 also receives anode exhaust, i.e. spent fuel andexcess fuel from fuel cells 40 which may comprise H₂, CO, H₂O, CO₂, andN₂, and discharges the anode exhaust from fuel cell manifold 32 throughan anode exhaust outlet 56 which is in fluid communication with arespective combustor 30. Similarly, fuel cell manifold 32 also receivescathode exhaust, i.e. spent air and excess air from fuel cells 40 whichmay comprise O₂ (depleted compared to the air supplied through first airsupply conduit 26 and second air supply conduit 28) and N₂, anddischarges the cathode exhaust from fuel cell manifold 32 through acathode exhaust outlet 58 which is in fluid communication with arespective combustor 30.

With continued reference to all of the FIGS. but now with emphasis onFIGS. 6, 8, and 9; combustor 30 may include an anode exhaust chamber 60which receives anode exhaust from anode exhaust outlet 56 of fuel cellmanifold 32, a cathode exhaust chamber 62 which receives cathode exhaustfrom cathode exhaust outlet 58 of fuel cell manifold 32, and acombustion chamber 64 which receives anode exhaust from anode exhaustchamber 60 and also receives cathode exhaust from cathode exhaustchamber 62. Anode exhaust chamber 60 may be substantially cylindricaland connected to anode exhaust outlet 56 through an anode exhaustpassage 66 which is coaxial with anode exhaust chamber 60. Anode exhaustchamber 60 includes a plurality of anode exhaust mixing passages 68which extend radially outward therefrom into combustion chamber 64.Cathode exhaust chamber 62 may be substantially annular in shape andradially surrounding anode exhaust passage 66 in a coaxial relationship.Cathode exhaust chamber 62 includes a plurality of cathode exhaustmixing passages 70 extending axially therefrom into combustion chamber64. Cathode exhaust mixing passages 70 are located proximal to anodeexhaust mixing passages 68 in order to allow anode exhaust gas exitinganode exhaust chamber 60 to impinge and mix with cathode exhaust exitingcathode exhaust chamber 62. Combustion of the mixture of anode exhaustand cathode exhaust may occur naturally due to the temperature withincombustion chamber 64 being equal to or greater than the autoignitiontemperature of the mixture of anode exhaust and cathode exhaust due tothe operation of fuel cell stack assemblies 20 or the operation of aplurality of electric resistive heating elements (not shown) that may beused to begin operation of fuel cell stack assemblies 20. In this way,anode exhaust is mixed with cathode exhaust within combustion chamber 64and combusted therein to form a heated combustor exhaust comprising CO₂,N₂, O₂, and H₂O. Combustor 30 includes a combustor exhaust outlet 72 atthe end of combustion chamber 64 for communicating the heated combustorexhaust from the combustor 30 to the interior volume of heater housing18 thereby heating heater housing 18 and subsequently formation 16.Using combustor 30 to generate heat for heating formation 16 allows fuelcell stack assemblies 20 to be operated is such a way that promotes longservice life of fuel cell stack assemblies 20 while allowing heaters 10to generate the necessary heat for heating formation 16.

With continued reference to all of the FIGS. and now with emphasis onFIGS. 6, 10, 11, and 12; each combustor 30 may include a flow director74 and heater 10 may include a baffle 76 positioned radially betweenfuel cell stack assemblies 20/combustors 30 and heater housing 18 inorder increase the effectiveness of transferring heat from the heatedcombustor exhaust to heater housing 18 and subsequently to formation 16.Baffle 76 is substantially cylindrical and coaxial with heater housing18, thereby defining a heat transfer channel 78, which may besubstantially annular in shape, radially between heater housing 18 andbaffle 76. As shown most clearly in FIG. 12, baffle 76 may be made ofmultiple baffle panels 80 (for clarity, only select baffle panels 80have been labeled) in order to ease assembly of heater 10. Baffle panels80 may be loosely joined together in order to prevent a pressuredifferential between heat transfer channel 78 and the volume that isradially inward of baffle 76. Baffle 76 includes a plurality of baffleapertures 82 (for clarity, only select baffle apertures 82 have beenlabeled) extending radially through baffle 76 to provide fluidcommunication from flow director 74 to heat transfer channel 78.

Flow director 74 includes a central portion 84 which is connected tocombustor exhaust outlet 72 and receives the heated combustor exhausttherefrom. Flow director 74 also includes flow director outlets 86 whichextend radially outward from central portion 84. Each flow directoroutlet 86 communicates with a respective baffle aperture 82 tocommunicate heated combustor exhaust to heat transfer channel 78. Afterbeing communicated to heat transfer channel 78, the heated combustorexhaust may pass upward through each heater 10 until reaching the top ofbore hole 14. Each flow director outlet 86 defines a flow director cleft88 with an adjacent flow director outlet 86. Flow director clefts 88allow various elements, e.g. first fuel supply conduit 22, second fuelsupply conduit 24, first air supply conduit 26, second air supplyconduit 28, and electrical conductors, to extend axially uninterruptedthrough heater housing 18. Flow director 74 may be made of a materialthat has good oxidation resistance, for example, stainless steel orceramic coated metal due to the high temperatures and corrosiveconditions flow director 74 may experience in use. In addition to flowdirector 74 and baffle 76 providing the benefit of placing the heatedcombustor exhaust where heat can be most effectively be transferred toformation 16, flow director 74 and baffle 76 provide the benefit ofsegregating fuel cell stack assemblies 20 from the heated combustorexhaust because fuel cell stack assemblies 20 may be sensitive to thetemperature of the heated combustor exhaust. In order to furtherthermally isolate fuel cell stack assemblies 20 from the heatedcombustor exhaust, baffle 76 may be made of a thermally insulativematerial or have a thermally isolative layer to inhibit transfer ofthermal energy from heat transfer channel 78 to fuel cell stackassemblies 20.

With continued reference to all of the FIGS. but now with emphasis onFIGS. 4, 5, 13, 14, 15, and 16; in addition to first fuel supply conduit22, second fuel supply conduit 24, first air supply conduit 26, andsecond air supply conduit 28 supplying fuel and air to fuel cell stackassemblies 20, first fuel supply conduit 22, second fuel supply conduit24, first air supply conduit 26, and second air supply conduit 28 alsoprovide structural support to fuel cell stack assemblies 20 withinheater 10. The lower end of heater housing 18 includes a support plate90 therein. Support plate 90 is of sufficient strength and securelyfastened to heater housing 18 in order support the weight of fuel cellstack assemblies 20, combustors 30 first fuel supply conduit 22, secondfuel supply conduit 24, first air supply conduit 26, second air supplyconduit 28 and baffle 76 that are located within heater 10. Supportplate 90 is arranged to allow the heated combustor exhaust from lowerheaters 10 to rise through each heater housing 18, much like a chimney,ultimately allowing the heated combustor exhaust to pass to the surfaceof formation 16.

First fuel supply conduit 22 and second fuel supply conduits 24 arecomprised of first fuel supply conduit sections 22 _(S) and second fuelsupply conduit sections 24 _(S) respectively which are positionedbetween support plate 90 and the lowermost fuel cell stack assembly 20within heater 10, between adjacent fuel cell stack assemblies 20 withina heater 10, and between the uppermost fuel cell stack assembly 20within a heater 10 and support plate 90 of the next adjacent heater 10.Similarly, first air supply conduit 26 and second air supply conduits 28are comprised of first air supply conduit sections 26 _(S) and secondair supply conduit sections 28 _(S) respectively which are positionedbetween support plate 90 and the lowermost fuel cell stack assembly 20within heater 10, between adjacent fuel cell stack assemblies 20 withina heater 10, and between the uppermost fuel cell stack assembly 20within a heater 10 and support plate 90 of the next adjacent heater 10.

Each fuel cell manifold 32 includes a first fuel supply boss 92 and asecond fuel supply boss 94. First fuel supply boss 92 and second fuelsupply boss 94 extend radially outward from fuel cell manifold 32 andinclude an upper fuel supply recesses 100 and a lower fuel supply recess102 which extend axially thereinto from opposite sides for receiving anend of one first fuel supply conduit section 22 _(S) or one second fuelsupply conduit section 24 _(S) in a sealing manner. Upper fuel supplyrecess 100 and lower fuel supply recess 102 of each first fuel supplyboss 92 and second fuel supply boss 94 are fluidly connected by a fuelsupply through passage 104 which extends axially between upper fuelsupply recess 100 and lower fuel supply recess 102. An upper fuel supplyshoulder 106 is defined at the bottom of upper fuel supply recess 100while a lower fuel supply shoulder 108 is defined at the bottom of upperfuel supply recess 100. In this way, first fuel supply conduit sections22 _(S) form a support column with first fuel supply bosses 92, therebysupporting fuel cell stack assemblies 20 and combustors 30 on supportplate 90 within heater housing 18. Similarly, second fuel supply conduitsections 24 _(S), form a support column with second fuel supply bosses94, thereby supporting fuel cell stack assemblies 20 and combustors 30on support plate 90 within heater housing 18. First fuel supply conduitsections 22 _(S) and second fuel supply conduit sections 24 _(S) may bemade of a material that is substantially strong to accommodate theweight of fuel cell stack assemblies 20 and combustors 30 within heater10. The material of first fuel supply conduit sections 22 _(S) andsecond fuel supply conduit sections 24 _(S) may also have properties towithstand the elevated temperatures within heater housing 18 as a resultof the operation of fuel cell stack assemblies 20 and combustors 30. Forexample only, first fuel supply conduit sections 22 _(S) and second fuelsupply conduit sections 24 _(S) may be made of a 300 series stainlesssteel with a wall thickness of 1/16 of an inch.

Fuel passing through first fuel supply conduit 22 and second fuel supplyconduit 24 may be communicated to fuel inlet 50 of fuel cell manifold 32via a fuel flow connecting passage 110 extending between fuel supplypass through passage 104 and fuel inlet 50. As shown, in FIG. 13, eachfuel cell manifold 32 may include only one fuel flow connecting passage110 which connects pass through passage 104 of either first fuel supplyboss 92 or second fuel supply boss 94 to fuel inlet 50. Also as shown,fuel cell manifolds 32 of adjacent fuel cell stack assemblies 20 mayinclude fuel flow connecting passage 110 in opposite first and secondfuel supply bosses 92, 94 such that every other fuel cell manifold 32receives fuel from first fuel supply conduit 22 while the remaining fuelcell manifolds 32 receive fuel from second fuel supply conduit 24.However; it should be understood that, alternatively, both first fuelsupply boss 92 and second fuel supply boss 94 of some or all of fuelcell manifolds 32 may include fuel flow connecting passage 110 in orderto supply fuel to fuel inlet 50 from both first fuel supply conduit 22and second fuel supply conduit 24.

Each fuel cell manifold 32 includes a first air supply boss 112 and asecond air supply boss 114. First air supply boss 112 and second airsupply boss 114 extend radially outward from fuel cell manifold 32 andinclude an upper air supply recesses 116 and a lower air supply recess118 which extend axially thereinto from opposite sides for receiving anend of one first air supply conduit section 26 _(S), or one second airsupply conduit section 28 _(S) in a sealing manner. Upper air supplyrecess 116 and lower air supply recess 118 of each first air supply boss112 and second air supply boss 114 are fluidly connected by an airsupply through passage 120 which extends axially between upper airsupply recess 116 and lower air supply recess 118. An upper air supplyshoulder 122 is defined at the bottom of upper air supply recess 116while a lower air supply shoulder 124 is defined at the bottom of lowerair supply recess 118. In this way, first air supply conduit sections 26_(S) form a support column with first air supply bosses 112, therebysupporting fuel cell stack assemblies 20 and combustors 30 on supportplate 90 within heater housing 18. Similarly, second air supply conduitsections 28 _(S), form a support column with second air supply bosses114, thereby supporting fuel cell stack assemblies 20 and combustors 30on support plate 90 within heater housing 18. First air supply conduitsections 26 _(S) and second air supply conduit sections 28 _(S) may bemade of a material that is substantially strong to accommodate theweight of fuel cell stack assemblies 20 and combustors 30 within heater10. The material of first air supply conduit sections 26 _(S) and secondair supply conduit sections 28 _(S) may also have properties towithstand the elevated temperatures within heater housing 18 as a resultof the operation of fuel cell stack assemblies 20 and combustors 30. Forexample only, first air supply conduit sections 26 _(S) and second airsupply conduit sections 28 _(S) may be made of a 300 series stainlesssteel with a wall thickness of 1/16 of an inch.

Supporting fuel cell stack assemblies 20 and combustors 30 from thebottom of heater housing 18 on support plate 90 results in the weightbeing supported by first air supply conduit sections 26 _(S), second airsupply conduit sections 28 _(S), first air supply conduit sections 26_(S), and second air supply conduit sections 28 _(S) in compressionwhich maximizes the strength of first air supply conduit sections 26_(S), second air supply conduit sections 28 _(S), first air supplyconduit sections 26 _(S), and second air supply conduit sections 28 _(S)and requires minimal strength of connection fasteners which join firstair supply conduit sections 26 _(S), second air supply conduit sections28 _(S), first air supply conduit sections 26 _(S), and second airsupply conduit sections 28 _(S). This also tends to promote sealingfirst air supply conduit sections 26 _(S), second air supply conduitsections 28 _(S), first air supply conduit sections 26 _(S), and secondair supply conduit sections 28 _(S) with fuel cell manifolds 32.Combining the structural support of fuel cell stack assemblies 20 andcombustors 30 by supply conduit sections 26 _(S), second air supplyconduit sections 28 _(S), first air supply conduit sections 26 _(S), andsecond air supply conduit sections 28 _(S) provides the furtheradvantage of avoiding additional structural components. Furthermore,supply conduit sections 26 _(S), second air supply conduit sections 28_(S), first air supply conduit sections 26 _(S), and second air supplyconduit sections 28 _(S) of a given heater 10 _(n) are independent ofall other heaters 10 in the sense that they only need to support fuelcell stack assemblies 20 and combustors 30 of heater 10 _(n), therebyrelying on heater housings 18 of heaters 10 as the principal support forheaters 10.

Fuel passing through first air supply conduit 26 and second air supplyconduit 28 may be communicated to air inlet 52 of fuel cell manifold 32via an air flow connecting passage 126 extending between air supply passthrough passage 120 and air inlet 52. As shown, in FIG. 14, each fuelcell manifold 32 may include only one air flow connecting passage 126which connects air supply through passage 120 of either first air supplyboss 112 or second air supply boss 114 to air inlet 52. Also as shown,fuel cell manifolds 32 of adjacent fuel cell stack assemblies 20 mayinclude air flow connecting passage 126 in opposite first and second airsupply bosses 112, 114 such that every other fuel cell manifold 32receives air from first air supply conduit 26 while the remaining fuelcell manifolds 32 receive air from second air supply conduit 28.However; it should be understood that, alternatively, both first airsupply boss 112 and second air supply boss 114 of some or all of fuelcell manifolds 32 may include air flow connecting passage 126 in orderto supply air to air inlet 52 from both first air supply conduit 26 andsecond air supply conduit 28.

When heaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n) are connected togetherin sufficient number and over a sufficient distance, the pressure offuel at fuel cell stack assemblies 20 may vary along the length ofheaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n). This variation in thepressure of fuel may lead to varying fuel flow to fuel cell stackassemblies 20 that may not be compatible with desired operation of eachfuel cell stack assembly 20. In order to obtain a sufficiently uniformflow of fuel to each fuel cell stack assembly 20, fuel flow connectingpassages 110 may include a fuel orifice 128 therein such that themagnitude of restriction provided by fuel orifice 128 is tailored to thelocation along heaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n) that aparticular fuel cell stack assembly 20 will be placed. In other words,fuel cell stack assemblies 20 that are closest to fuel reformer 48 mayhave fuel orifice 128 that is configured to provide a restriction ofmagnitude RF₁ while fuel cell stack assemblies 20 that are furthest fromfuel reformer 48 may be configured to provide a restriction of magnitudeRF₂ where RF₁>RF₂. In this way, fuel orifices 128 that are configured toprovide restriction of magnitude RF₂ are subjected to lower fuelpressure due to being a greater distance from fuel reformer 48.Consequently, fuel orifices 128 that have restriction of magnitude RF₂provide less restriction in order to closely match the fuel flow throughfuel orifices 128 that are configured to provide restriction ofmagnitude RF₁ which are subjected to higher fuel pressure, therebyproviding less variation in fuel flow to each fuel cell stack assembly20. In order provide sufficient uniformity of fuel flow to fuel cellstack assemblies 20, it may be necessary to arrange fuel cell stackassemblies 20 in fuel cell stack assembly groups 129 ₁-129 _(m) wherefuel cell stack assembly group 129 ₁ is closest to fuel reformer 48,fuel cell stack assembly group 129 _(m) is furthest from fuel reformer48, m is the total number of fuel cell stack assembly groups 129, andeach fuel cell stack assembly group 129 _(x) (x is from 1 to m) usesfuel orifice 128 configured to provide a restriction of magnitude RF_(x)(x is from 1 to m) that is unique to fuel cell stack assembly group 129_(x). FIG. 18 has been included which shows fuel cell stack assemblygroup 129 ₁, fuel cell stack assembly group 129 _(m−1) and fuel cellstack assembly group 129 _(m). Each fuel cell stack assembly group 129_(x) may each contain equal quantities of fuel cell stack assemblies 20;however, it may be preferable for at least one fuel cell stack assemblygroup 129 _(x) to contain a different number of fuel cell stackassemblies 20. For example, when heaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10_(n) include a total of 333 fuel cell stack assemblies 20, fuel cellstack assemblies 20 may be arranged in three fuel cell stack assemblygroups 129 ₁, 129 ₂, and 129 ₃ where there are 55 fuel cell stackassemblies 20 in fuel cell stack assembly group 129 ₁, 55 fuel cellstack assemblies 20 in fuel cell stack assembly group 129 ₂, and 223fuel cell stack assemblies 20 in fuel cell stack assembly group 129 ₃.It should be noted that fuel cell stack assemblies 20 in fuel cell stackassembly group 129 ₁ use fuel orifices 128 configured to provide a firstmagnitude of restriction, fuel cell stack assemblies 20 in fuel cellstack assembly group 129 ₂ use fuel orifices 128 configured to provide asecond magnitude of restriction that is less than the magnitude ofrestriction provided by fuel orifices 128 of fuel cell stack assemblygroup 129 ₁, and fuel cell stack assemblies 20 in fuel cell stackassembly group 129 ₃ use fuel orifices 128 configured to provide a thirdmagnitude of restriction that is less than the magnitude of restrictionprovided by fuel orifices 128 of fuel cell stack assembly group 129 ₂.In general terms, the magnitude of restriction provided by fuel orifices128 in fuel cell stack assembly group 129 _(x−1) is less than themagnitude of restriction provided by fuel orifices 128 in fuel cellstack assembly group 129 _(x). For the same 333 fuel cell stack assemblyexample, fuel cell stack assemblies 20 may be arranged into more thanthree fuel cell stack assembly groups 129 in order to further reducefuel flow variation to fuel cell stack assemblies 20, however, doing sorequires a greater number of fuel orifices 128 configured to providedifferent magnitudes of restriction which may make it more difficult toassemble heaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n) due to the need tokeep fuel cell stack assemblies 20 in proper order. Similarly, for thesame 333 fuel cell stack assembly example, fuel cell stack assemblies 20may be arranged into fewer than three fuel cell stack assembly groups129 in order to reduce the number of different fuel cell stackassemblies 20 to keep track of during assembly of heaters 10 ₁, 10 ₂, .. . 10 _(n−1), 10 _(n); however, a tradeoff will be made in greater fuelflow variation to fuel cell stack assemblies 20. Consequently, thenumber of fuel cell stack assembly groups 129 is determined at least inpart by the total number of fuel cell stack assemblies 20 in heaters 10₁, 10 ₂, . . . 10 _(n−1), 10 _(n), the length of heaters 10 ₁, 10 ₂, . .. 10 _(n−1), 10 _(n), and the extent to which fuel pressure variationcan be tolerated between fuel cell stack assemblies 20.

In order for fuel orifice 128 to achieve the desired magnitude ofrestriction, fuel orifice 128 may be sized to provide the desiredmagnitude of restriction. More specifically, fuel orifice 128 is madelarger to provide a smaller magnitude of restriction and fuel orifice128 is made smaller to provide a larger magnitude of restriction.Alternatively, as shown in FIG. 19, multiple fuel orifices 128 may beprovided in series in fuel flow connecting passage 110. By providingmultiple fuel orifices 128 in fuel flow connecting passage 110, eachfuel orifice 128 may be made larger in order to ease manufacturing andto reduce tendency to plug while achieving the desired magnitude ofrestriction.

In order to vary the electricity and/or thermal output of fuel cellstack assemblies 20, the composition of the fuel may be varied in orderto achieve the desired electricity and/or thermal output of fuel cellstack assemblies 20. As described previously, fuel is supplied to fuelcell stack assemblies 20 by fuel reformer 48. Fuel reformer 48 mayreform a hydrocarbon fuel, for example CH₄, from a hydrocarbon fuelsource 130 to produce a blend of H₂, CO, H₂O, CO₂, N₂, CH₄. The portionof the blend which is used by fuel cell stack assemblies 20 to generateelectricity and heat is H₂, CO, and CH₄ which may be from about 10% toabout 90% of the blend. Fuel reformer 48 may be operated to yield aconcentration of H₂, CO, and CH4 that will result in the desiredelectricity and/or thermal output of fuel cell stack assemblies 20.Furthermore, a dilutant such as excess H₂O or N₂ may be added downstreamof fuel reformer 48 from a dilutant source 131 to further dilute thefuel. In this way, the fuel composition supplied to fuel cell stackassemblies 20 may be varied to achieve a desired electricity and/orthermal output of fuel cell stack assemblies 20.

Similarly, when heaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n) areconnected together in sufficient number and over a sufficient distance,the pressure of air at fuel cell stack assemblies 20 may vary along thelength of heaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n). This variationin the pressure of air may lead to varying air flow to fuel cell stackassemblies 20 that may not be compatible with desired operation of eachfuel cell stack assembly 20. In order to obtain a sufficiently uniformflow of air to each fuel cell stack assembly 20, air flow connectingpassages 126 may include an air orifice 132 therein such that themagnitude of restriction provided by air orifice 132 is tailored to thelocation along heaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n) that aparticular fuel cell stack assembly 20 will be placed. In other words,fuel cell stack assemblies 20 that are closest to air supply 54 may haveair orifice 132 that is configured to provide a restriction of magnitudeRA₁ while fuel cell stack assemblies 20 that are furthest from airsupply 54 may be configured to provide a restriction of magnitude RA₂where RA₁>RA₂. In this way, air orifices 132 that are configured toprovide restriction of magnitude RA₂ are subjected to lower air pressuredue to being a greater distance from air supply 54. Consequently, airorifices 132 that have restriction of magnitude RA₂ provide lessrestriction in order to closely match the air flow through air orifices132 that are configured to provide restriction of magnitude RA₁ whichare subjected to higher air pressure, thereby providing less variationin air flow to each fuel cell stack assembly 20. In order providesufficient uniformity of air flow to fuel cell stack assemblies 20, eachfuel cell stack assembly group 129 _(x) (x is from 1 to m where fuelcell stack assembly group 129 ₁ is closest to air supply 54 and fuelcell stack assembly group 129 _(m) is furthest from air supply 54) usesair orifice 132 which is configured to provide restriction of magnitudeRA_(x) (x is from 1 to m) that is unique to fuel cell stack assemblygroup 129 _(x). In the example of heaters 10 ₁, 10 ₂, . . . 10 _(n−1),10 _(n) including a total of 333 fuel cell stack assemblies 20, fuelcell stack assemblies 20 in fuel cell stack assembly group 129 ₁ use airorifices 132 configured to provide a first magnitude of restriction,fuel cell stack assemblies 20 in fuel cell stack assembly group 129 ₂use air orifices 132 configured to provide a second magnitude ofrestriction that is less than the magnitude of restriction provided byair orifices 132 of fuel cell stack assembly group 129 ₁, and fuel cellstack assemblies 20 in fuel cell stack assembly group 129 ₃ use airorifices 132 configured to provide a third magnitude of restriction thatis less than the magnitude of restriction provided by air orifices 132of fuel cell stack assembly group 129 ₂. In general terms, the magnitudeof restriction provided by air orifices 132 in fuel cell stack assemblygroup 129 _(x+1) is less than the magnitude of restriction provided byair orifices 132 in fuel cell stack assembly group 129 _(x).

In order for air orifice 132 to achieve the desired magnitude ofrestriction, air orifice 132 may be sized to provide the desiredmagnitude of restriction. More specifically, air orifice 132 is madelarger to provide a smaller magnitude of restriction and air orifice 132is made smaller to provide a larger magnitude of restriction.Alternatively, as shown in FIG. 20, multiple air orifices 132 may beprovided in series in air flow connecting passage 126. By providingmultiple air orifices 132 in air flow connecting passage 126, each airorifice 132 may be made larger in order to ease manufacturing and toreduce tendency to plug while achieving the desired magnitude ofrestriction.

In use, heaters 10 ₁, 10 ₂, . . . 10 _(n−1), 10 _(n) are operated bysupplying fuel and air to fuel cell stack assemblies 20 which arelocated within heater housing 18. Fuel cell stack assemblies 20 carryout a chemical reaction between the fuel and air, causing fuel cellstack assemblies 20 to be elevated in temperature, for example, about600° C. to about 900° C. The anode exhaust and cathode exhaust of fuelcell stack assemblies 20 is mixed and combusted within respectivecombustors 30 to produce a heated combustor exhaust which is dischargedwithin heater housing 18. Consequently, fuel cell stack assemblies 20together with the heated combustor exhaust elevate the temperature ofheater housing 18 with subsequently elevates the temperature offormation 16.

While this invention has been described in terms of preferredembodiments thereof, it is not intended to be so limited, but ratheronly to the extent set forth in the claims that follow.

We claim:
 1. A heater assembly comprising: a plurality of fuel cellstack assemblies which each have a plurality of fuel cells which convertchemical energy from a fuel into heat and electricity through a chemicalreaction with an oxidizing agent, each one of said plurality of fuelcell stack assemblies having a fuel cell manifold which 1) receives saidfuel within a fuel inlet of said fuel cell manifold and distributes saidfuel to said plurality of fuel cells and 2) receives said oxidizingagent within an oxidizing agent inlet of said fuel cell manifold anddistributes said oxidizing agent to said plurality of fuel cells; a fuelsupply conduit in fluid communication with said fuel cell manifold ofsaid plurality of fuel cell stack assemblies, thereby communicating saidfuel to said fuel inlet of said fuel cell manifold of said plurality offuel cell stack assemblies; and an oxidizing agent supply conduit influid communication with said fuel cell manifold of said plurality offuel cell stack assemblies, thereby communicating said oxidizing agentto said oxidizing agent inlet of said fuel cell manifold of saidplurality of fuel cell stack assemblies; wherein each of said pluralityof fuel cell stack assemblies includes an orifice disposed between saidfuel supply conduit and said fuel inlet or between said oxidizing agentsupply conduit and said oxidizing agent inlet; and wherein saidplurality of fuel cell stack assemblies are arranged in fuel cell stackassembly groups such that said orifices of each of said fuel cell stackassembly groups are configured to provide a magnitude of restrictionthat is unique to their respective said fuel cell stack assembly group,thereby providing uniformity of flow of said fuel or said oxidizingagent to said plurality of fuel cell stack assemblies.
 2. A heaterassembly as in claim 1 wherein: said fuel supply conduit is configuredto receive said fuel from a fuel source; said oxidizing agent supplyconduit is configured to receive said oxidizing agent from an oxidizingagent source; and said magnitude of restriction of said orifices of saidfuel cell stack assembly groups that are closer to said fuel source orsaid oxidizing agent source is greater than said magnitude ofrestriction of said orifices of said fuel cell stack assembly groupsthat are farther from said fuel source or said oxidizing agent source.3. A heater assembly as in claim 2 wherein each one of said fuel cellstack assembly groups that are closer to said fuel source or saidoxidizing agent source contain a lesser or equal number of saidplurality of fuel cell stack assemblies than each one of said fuel cellstack assembly groups that are farther from said fuel source or saidoxidizing agent source.
 4. A heater assembly as in claim 2 wherein saidorifices of said fuel cell stack assembly groups that are closer to saidfuel source or said oxidizing agent source are smaller than saidorifices of said fuel cell stack assembly groups that are farther fromsaid fuel source or said oxidizing agent source.
 5. A heater assembly asin claim 1 wherein: said fuel supply conduit is configured to receivesaid fuel from a fuel source; said oxidizing agent supply conduit isconfigured to receive said oxidizing agent from an oxidizing agentsource; and each one of said fuel cell stack assembly groups that arecloser to said fuel source or said oxidizing agent source contain anequal or greater number of said plurality of fuel cell stack assembliesthan said fuel cell stack assembly groups that are farther from saidfuel source or said oxidizing agent source.
 6. A heater assembly as inclaim 1 wherein said plurality of fuel cell stack assemblies of at leastone of said fuel cell stack assembly groups includes a plurality of saidorifices disposed in series between said fuel supply conduit and saidfuel inlet or between said oxidizing agent supply conduit and saidoxidizing agent inlet.
 7. A heater assembly as in claim 1 wherein: saidheater assembly is disposed within a bore hole of a formation, said borehole extending from a top end to a bottom end; and said magnitude ofrestriction of said orifices of said fuel cell stack assembly groupsthat are closer to said top end is greater than said magnitude ofrestriction of said orifices of said fuel cell stack assembly groupsthat are farther from said top end.
 8. A heater assembly as in claim 7wherein each one of said fuel cell stack assembly groups that are closerto said top end contain a lesser or equal number of said plurality offuel cell stack assemblies than each one of said fuel cell stackassembly groups that are farther from said top end.
 9. A heater assemblyas in claim 7 wherein said orifices of said fuel cell stack assemblygroups that are closer to said top end are smaller than said orifices ofsaid fuel cell stack assembly groups that are farther from said top end.